Exactly Mike.
It's all dependant on how many are first discovered, and what appeals at that time, or is fashionable.
You can say there are 4 types of the 1908, or not bother at all and say there is just one type.
If the latter, then there is no 1926ME, 1911 hollow neck, 1903 open 3 etc. The 1874 series would be half as big.....
What about the 1890 dropped 90? Try finding one.....
I have an 1880 with sea by the ship missing. So what.
But, if it's a 1934, everyone is interested.
You have to have that 'magic ammount' found- not quite enough to go round, but _just_ enough discovered
for people to feel they are missing out by not having one......!
( The exception to this is when clearly there was a _set_ of dies made, but one obviously missing.
An 1862 halfpenny with a 'D', or more spectacularly, an 1863 with a clear '1' below the date turns up.....see what happens....)